US 48 is the designation for Corridor H of the Appalachian Development Highway System. Corridor H is a highway through the Appalachian Mountains that, when completed, will connect I-79 in West Virginia to I-81 in Virginia. The sections of the highway that have been constructed so far are entirely in West Virginia. However, the US 48 designation extends into Virginia to where the highway is proposed to end at I-81. The section in Virginia is a two-lane surface road that is multiplexed with VA 55 for its entire length. The section in Frederick County is known as Wardensville Pike, while the section in Shenandoah County is known as John Marshall Highway.